00:01
If we have f of x equals negative x squared plus bx plus 8, then if we factor out a negative from the first two terms dealing with x, we have negative of x squared minus bx, leaving the spot to complete the square plus 8.
00:16
Now if we complete the square, we take half of negative b, which is negative b over 2 and square, it would be plus b squared over 4.
00:24
But then when you think of how we're affecting the right hand side, we're really scaling it by negative b squared over 4.
00:30
So we have, we have to be really scaling it by negative b squared over 4.
00:31
Have to then add it again so that we're back to where we were.
00:37
So now we can write this in vertex form negative of x minus b over 2 squared plus 8 plus b squared over 4, which from this our vertex is going to be at b over 2 comma 8 plus b squared over 4.
01:01
Now the vertex we know has a second coordinate of 17.
01:09
So we would know that 17 is equal to 8 plus b squared over 4...